The thermal barrier function and function of cooling the friction elements of mechanical packing are performed by tappings (ducts with (an) inlet(s) and (an) outlet(s) that feed certain zones are defined as tappings) arranged in the pump housing, the mechanical packing and in the fluid header if there is one. Existing techniques make maintenance difficult because piping has first of all to be removed. Moreover, having numerous tappings in standard components increases costs, notably because of the need to make the holes and weld on the supply piping. Furthermore, the cooling water comes from two different circuits, namely an auxiliary cooling circuit used for the thermal barrier function and another circuit for cooling the friction elements of the mechanical packing using water from the pump and an external heat exchanger.
Such devices make sealing-device maintenance difficult in so far as the tappings are made in the mechanical packing and in the pump housing.
That being the case, the problem set here is that of producing a pump sealing device of the abovementioned type, which is of simple construction and facilitates maintenance of said device and improves the life of the device. The present invention also seeks to combine two functions into one and the same single sealing device where there is just one cooling circuit the purpose of which is to cool the friction elements of the mechanical packing and to form a thermal barrier that protects the mechanical packing from heat, so as to lengthen the life of the device. The mechanical packing provides sealing at the end of a shaft and on the outside of the pump housing. The temperature of the mechanical packing and of the water flowing near the mechanical packing must not exceed a threshold temperature, conventionally 100° C. Now, typically, the water circulating through the pump is at a temperature of around 200° C. Bearing in mind the mechanical properties of the packing and notably of the stationary and rotating face rings (the stationary and rotating friction elements of the mechanical packing are defined as the stationary and rotating face rings) and how they are arranged in the sealing device, it is important to protect them from excessive heat in order to protect them from degradation. What happens is that an exchange of heat by conduction between the pump housing and the mechanical packing may impair correct operation of the seal and notably may impair sealing at the point between the stationary face ring and the rotating face ring. Moreover, friction between the rotating part of the mechanical packing defined by the rotating face ring of the packing on the one hand, and the stationary part defined by the stationary face ring of the packing on the other hand, dissipates energy in the form of heat, leading to a rise in temperature and to premature wear of the stationary and rotating face rings. Thus, in order to lengthen the life of the mechanical packing, provision is made for the mechanical packing to be cooled at the places where the friction occurs, namely at that point in the mechanical packing and, more specifically, at the point where there is relative motion between the rotating face ring and the stationary face ring.
Furthermore, the present invention seeks notably to optimize the maintenance of the sealing device and to lengthen the life of the sealing device. Another object of the present invention is to reduce the number of components that make up the sealing device and at the same time to reduce the costs of manufacturing a pump sealing device.
The solution proposed by the present invention is that the device for sealing a pump comprises:                a pump housing comprising first and second ducts for the passage of a fluid;        a shaft comprising, near the pump housing, a first passage for the fluid;        a mechanical packing mounted between the shaft and the pump housing and comprising friction elements for the rubbing-together of a rotating part and of a stationary part,        said device having two states, a shut down first state in which no fluid circulates through said device and an operating second state in which the fluid flows in a flow circuit passing via:        the first passage to supply the circuit with fluid,        a second passage comprised between the pump housing and the packing and communicating with said friction elements, the second passage then forming a means of cooling the friction elements and a thermal barrier,        the first duct to supply the second passage with cooled fluid,        the second duct to remove the hot fluid from the second passage.        
Such an arrangement advantageously allows maintenance to be made easier and allows the life of the sealing device to be lengthened while at the same time reducing the number of components that make up the device and the cost of manufacturing such a component. The pump housing, the shaft and the mechanical packing together incorporate a means of cooling the friction elements and a thermal barrier, which therefore need to be supplied with fluid. The present invention proposes using a single circuit to supply both the means for cooling the friction elements and the thermal barrier via the second passage. Some of the fluid circulating through the second passage has the function of cooling the mechanical packing adjacent to this second passage, so as to lower the temperature of the friction elements therefore allowing pump usage with no risk of leakage; this then prevents pump water from coming into contact with the external surroundings. Another proportion of the fluid circulating through the second passage has the function of forming a thermal barrier so as to protect the packing, notably the friction elements thereof, from the heat dissipated by the pump housing and caused by the hot water circulating through said pump.
The flow circuit followed by the fluid advantageously makes it possible to reduce the number of components of which the device is made. More specifically, all the arrangements of pump housing, shaft and packing, correlated with the fluid circuit offers the benefit of a reduced number of components while at the same time offering optimized means of protecting the packing and the friction elements thereof.
In one embodiment, a first chamber extends radially between the packing and the pump housing and axially between the cover and a fourth passage.
In one embodiment, the device might comprise a second chamber comprised between the pump housing on the one hand and the packing on the other and might define, in the operating state, a second thermal barrier.
In another embodiment, the above-mentioned second chamber is bounded:                radially, by the shaft and a bore formed in the pump housing,        axially, by the packing and the pump housing.        
In another embodiment, a gap runs longitudinally between the shaft and the pump housing, said gap running circumferentially and defining, in the operating state, a third thermal barrier.
In yet another embodiment, the pump housing might comprise a third passage providing communication between said second and third thermal barriers.
In another embodiment of the invention, the third passage immediately faces, in the axial direction, the lateral part of the stationary face ring.
In another embodiment, a first passage between the shaft and the pump housing is intended for circulating the fluids from the pump toward the gap.
In one embodiment, the second passage might comprise said first and second chambers, the fourth passage, a third passage providing communication between the second chamber and the gap, and the gap.
In yet another embodiment, the second operating state is triggered by the shaft beginning to rotate.
In another embodiment of the invention, the sealing device further comprises a fluid-cooling device connected to first and second ducts.